A CCD sensor used for electronic imaging applications typically includes both horizontal and vertical shift registers (internal to the sensor structure) to supply charge levels indicative of individual pixels in a scanned image to external equipment such as a frame store controlling a video monitor. At the end of the horizontal shift register, an output amplifier is provided to drive all necessary output signal processing circuits. The output from the sensor's horizontal shift register, and hence from its output amplifier, takes the form of a square wave having a frequency equal to the horizontal clock frequency of the sensor. A correlated double sample and hold (CDS/H) circuit is normally also connected to receive the square wave sensor output, detect the difference between the pre-charge level of that output and the signal levels representing individual pixel images, and serve as a low pass filter. Often, the CDS/H circuit lacks sufficient driving capacity. For that reason, a transistor emitter follower (which has a high input impedance and a low output impedance) is commonly connected to receive the CDS/H circuit output and provide a necessary impedance transformation function and, thereby, the needed driving capacity.
In one important example, the output of the CDS/H circuit has one or two volts of d-c bias. A transistor emitter follower driven from the CDS/H circuit is then operated with dual power supplied (one connected to the collector of the transistor and another, of opposite polarity, connected to the emitter of the transistor through a load resistor) in order to avoid clipping. With the emitter follower impedance transformation circuits found in the prior art, such an arrangement introduces problems of power dissipation. Recently developed CCD image sensors, moreover, have multiple outputs and, for that reason, need as many CDS/H circuits and emitter followers as they have outputs. In such multiple emitter follower arrangements, power dissipation problems are correspondingly larger and, because of heat build up around the sensor and a resulting increase in sensor temperature, tend to cause so-called dark current problems in the CCD sensor. A better way of powering the transistor emitter followers receiving the outputs of multiple output CCD image sensors is, therefore, highly desirable.